A male coupling member and a female coupling member of a pipe coupling are commonly equipped with an on-off valve that closes a fluid passage formed through the male and female coupling members to prevent fluid from flowing out therefrom when the coupling members are decoupled from each other. In the decoupled state, if a hose connected to the coupling members is, for example, twisted, an excessively high internal pressure may be generated therein. If the coupling members are recoupled together in such a state, the fluid rapidly flows around the on-off valve as it slightly opens. Such rapid flow of fluid creates a negative pressure around the surface of the on-off valve that has just separated from the associated annular valve seat surface. The negative pressure causes a seal ring provided on the valve surface to be deformed toward the fluid passage. The seal ring thus deformed is subjected to excessive force from the fluid and hence likely to separate from the on-off valve.
There have been developed a variety of coupling members adapted to enable the internal pressure to be removed from the coupling members before they are coupled together (see, for example, Japanese Utility Model Registration Application Publication No. Sho 50-124624). The main purpose of pressure removal in this case is to solve the problem that when the internal pressure is high, it is difficult to push open the on-off valve because of the high internal pressure
when the male and female coupling members are put to each other to couple them together.
In a pipe coupling used in a die-casting machine or the like, however, strong force is applied to couple the coupling members. Therefore, even if the pressure in the coupling members is rather high, the on-off valve can be pushed in to couple the coupling members. In this case, the high-pressure fluid remaining in the coupling member rapidly flows around the on-off valve, and the seal ring is likely to separate, as has been stated above.
There is likelihood of the seal ring being separated under any circumstances where the fluid rapidly flows around the on-off valve, not only when the coupling members are coupled together as stated above.
The present invention has been made in view of the above-described conventional technique. Accordingly, an object of the present invention is to provide a coupling member adapted to minimize the occurrence of separation of the seal ring by the rapid flow of fluid around the on-off valve when it is opened.
FIG. 1 shows a seal ring 12 used in a conventional on-off valve 10, that is, a seal ring with a rectangular section that is fitted and fixed in an annular groove 16 formed on a valve head 14. The inventor of this application considered that the configuration of this seal ring also relates to the separation of the seal ring, and improved the seal ring configuration to provide a pipe coupling adapted so that separation of the seal ring is unlikely to occur.